This invention relates to the monitoring of a halocarbon vapor compression refrigerant system and more specifically to apparatus which is adapted to respond to the presence of non-condensable contaminant gases in the system to purge them from the system and which may also advantageously provide an indication of the onset of a system malfunction in time to initiate corrective action before actual system breakdown occurs.
Refrigerant systems of the type which can advantageously employ the present invention are those used in air conditioners, heat pumps, commercial food refrigeration systems and the like, which employ a sealed refrigerant circuit comprised of a refrigerant compressor, a condenser, an evaporator and a fluid expansion device, such as an expansion valve or a capillary tube, connected between the condenser and the evaporator. Such systems may also include a filter-drier to remove particulate contaminants and to control the moisture content of the circulating refrigerant. Such systems may also include a receiver for controlling and metering the flow of liquid refrigerant from the condenser and an accumulator located upstream of the suction line leading to the compressor, the purpose of the receiver being to store excess liquid refrigerant in the system and to avoid influx of the liquid refrigerant to the compressor during start-up.
Systems of the type just described are called hermetic systems or semi-hermetic systems because they are designed to operate most effectively by the rigorous exclusion of air or other contaminant gases in the sealed system. Hermetic systems are thoroughly evacuated during the final stages of manufacture and are permanently sealed, usually by soldering or brazing, after the refrigerant charge is introduced into the unit. Some air conditioners and heat pumps are installed as split systems, requiring final assembly in the field. In these systems, the internal heat exchanger is remote from the compressor unit, which is located outside of the structure or dwelling to be conditioned. In the installation of these split systems, precautions for eliminating contaminant gases are exercised, though these are not as effective as those employed in factory sealed hermetic systems. Semi-hermetic systems are generally larger systems with provisions for unbolting the compressor case to facilitate replacement of compressor parts or the hermetic motor, if such repair is necessary. In systems of this type, the vapor compression or refrigerant circuit is designed to operate with only the halocarbon working fluid and selected lubricating oil charged into the sealed system.
For larger systems, particularly for industrial or commercial engineered refrigeration systems, means for purging the system of contaminant gases may be required. If the system operates below atmospheric pressure, any leaks such as through gaskets and seals will permit entry of air into the refrigerant system. Surge-type receivers have been used in the design of these halocarbon refrigerant systems and these are often provided with a purge valve on the condenser to facilitate removal of contaminant gases. When these purge valves are opened to release contaminant gases, loss of halocarbon refrigerant also is likely since there is no means for separation of the gases released from the system. Loss of refrigerant may be harmful to the operation of the system, if the system is charge sensitive, and inadvertent discharging of certain refrigerants to the atmosphere may have harmful environmental consequences.
Systems utilizing ammonia as refrigerant fluid have employed a non-condensable gas separator as an accessory, as illustrated, for example, in U.S. Pat. No. 1,636,512. These types of purge units tend to be complex assemblies of drums, coils, valves and piping connections, however, and are not known to be employed in halocarbon refrigerant systems.
Practical experience with many sealed refrigeration systems operating over long periods has demonstrated that properly designed and installed vapor compression systems are free from contaminant gases. In those instances when contaminant gases are present, they may interfere with the performance or reliability of the system. The presence of non-condensable gases in vapor compression systems results in reduced efficiency or, in more severe cases, in catastrophic failure of the motor-compressor. Reduced efficiency results because the compressor circulates non-condensable gases through the system which results in non-productive work being performed.
Sources of contaminant gases in vapor compression systems are several. A likely source arises from incomplete evacuation of air and this source is most pronounced in field assembled split-systems. Even when evacuation is very thorough, some materials of construction continue to outgas at a slow rate for some time after evacuation pumping has ceased. Another source of contaminant gases arises from low side leaks. Although hermetic systems are carefully leak-checked during assembly, very small leaks sometimes escape detection. If these leaks are located in the low pressure side of the system and if the system design is such that the low side operating pressure is less than atmospheric pressure, air will be drawn into the sealed system at a rate determined by the pressure differential and the size of the leak. A final source of contaminant gases arises from decomposition products generated inside the refrigerant system if the system, and particularly the motor-compressor unit, is allowed to operate at conditions of high temperature or marginal lubrication. It is known that larger quantities of these products are produced as operating conditions become more severe and that, ultimately, system failure will result.
Systems of the type described above generally are operated with no provision for determining incipient malfunctions in the system, although a moisture indicator has been used in some installations. Typically, the system is operated until system breakdown occurs at which time repair service is initiated to put the system back into operation. The down time that results from this kind of reactive maintenance program is, at best, an inconvenience for the system user and can often be very costly in terms of such things as food spoilage, as in the case of commercial food refrigeration systems. It is, therefore, desirable to provide apparatus that will monitor the operation of the refrigerant system on an ongoing basis to provide an indication of the onset of a system malfunction caused by the presence of non-condensable contaminant gases and/or to purge the system of such gases to realize more efficient system operation and to minimize maintenance requirements.
It is therefore an object of the invention to provide a monitor for a halocarbon vapor compression refrigerant system that provides for in-situ indication of an incipient malfunction in the system's operation caused by the presence of non-condensable contaminant gases.
It is a further object of the invention to provide apparatus that will continuously and automatically monitor the halocarbon refrigerant system for the presence of non-condensable contaminant gases and remove them from the system without undesired removal of the halocarbon fluid.
It is yet a further object of the invention to provide apparatus which is capable of continuously and automatically monitoring a halocarbon refrigerant system to purge the refrigerant circuit of contaminant gases and simultaneously providing an indication of the presence and build-up of the contaminant gases so as to serve as a warning of an incipient malfunction requiring repair service before breakdown occurs.
It is a still further object of the invention to provide apparatus of the type described which is simple to implement and does not require highly skilled technicians in the field to operate and maintain.